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C-130 Hercules dropping pallet with Low Altitude Parachute Extraction System on Khe Sanh runway.


A C130 performing a Low Altitude Parachute Extraction.

An M551 Sheridan being dropped from a C-130 Hercules.

Low Altitude Parachute Extraction System (LAPES) is a tactical military airlift delivery method where a fixed wing cargo aircraft can deposit supplies when landing is not an option in an area that is too small to accurately parachute supplies from a high altitude.

This method was developed by the US Military with the assistance of the 109th Quartermaster Company (Air Drop) in 1964. In May 1965, a detachment of the 109th was formed as the 383rd Quartermaster (Aerial Supply) Detachment and sent to Vietnam. In 1966 the 109th was sent to Vietnam and took operational control of the 383rd. Both units provided Air Drop and LAPES support during the Siege of Khe Sanh in the Vietnam War. LAPES was used to provide a method of supplying heavy loads into Khe Sanh which could not effectively be supplied by air drop.[1] This practice was perfected at Mactan Air Base in Cebu, the Philippines.

LAPES involves loading supplies on a special pallet on a plane. In preparation for a drop the cargo door and ramp of the aircraft is opened and a drogue parachute released. The aircraft descends to the drop altitude (typically only a few metres above the ground). Once the drop plane reaches the desired drop point, the braking parachutes for the load are released and they are extracted from the aircraft by the drogue chute and the drop load is released (retaining straps cut). The braking parachutes pull the load from the aircraft and bring it to a stop on the ground within the drop zone. The main parachutes are sized to stop the movement of the load sliding on the ground within the required space, and are not intended to control the descent of the load to the ground. Cushioning of the load is accomplished by the pallet and the material between the pallet and the load. Once the delivery is accomplished, the pilot ascends to a normal altitude and returns to base.

LAPES enables planes to quickly deploy large cargo in a timely fashion instead of having to land and take off, which exposes the plane to enemy fire. The technique also allows delivery of loads that are too heavy for a direct parachute descent (high altitude drop). However, the drop sequence's low altitude allows for no margin of pilot error and the risk of plane crash is heightened.[1]

On July 1, 1987 during a Capabilities exercise (CAPEX) a USAF C-130E (68-10945 c/n 4325) crashed while performing a LAPES demo at the Sicily Drop Zone, on Ft. Bragg. The pilot of the C-130 had performed a LAPES drop with the same extreme rate of descent two days earlier during a practice run. The crash killed three on board, one soldier on the ground, and injured two crew.[2]

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